1. Field of the Invention
The present invention relates to a displacement detection apparatus for optically detecting a small movement of an object in an industrial manufacturing apparatus or the like in a non-contact state, and a magnetic recording apparatus as an industrial product manufacturing apparatus using the displacement detection apparatus.
2. Related Background Art
For example, in the process of magnetically recording a servo pattern on the surface of a disk in a hard disk device (HDD) used in a computer, the position of the magnetic head must be sequentially shifted by a predetermined amount.
The positioning resolving power requires an accuracy in the order of several nm, consonant with the increase in density of an HDD. To realize such positioning in the order of several nm, a resolving power and stability greater than those of a laser interferometric measuring machine are required. In recent years, a grating interference rotary encoder has been used.
FIG. 1 is a schematic view of a conventional positioning apparatus for servo track signal writing.
A rotary positioner 1 is constructed by a positioning control motor 2, a rotary encoder 3 attached to the motor 2 to detect the rotation amount of the rotating shaft, an arm 4, and a pushrod 5 projecting from the distal end portion of the arm 4.
The rotary positioner 1 is connected to a computer 7 through a control system 6.
In operation, while rotating and sequentially feeding the arm 4 in a small amount to position it by the rotary positioner 1, a small current is supplied to a voice coil motor 8 to move a head arm 9 and bring it into contact with the pushrod 5.
Hence, the movement of the head arm 9 matches that of the pushrod 5. When vibration by rotation of the hard disk is transmitted to the head arm 9 and then to the motor 2 through the cylindrical surface of the pushrod 5, highly accurate positioning by the rotary positioner system is impeded so as to deteriorate the writing performance for information, such as servo track signals at a high density.
Various kinds of methods using an optical sensor for optically detecting the head arm 9 itself in a non-contact state at an nm-order resolving power stability have also been examined.
However, since these methods require an expensive diffraction grating on the head arm 9 or special working, a demand has arisen for a more inexpensive and effective method.